New Type of Organic Alloys: Modification of Phase Transition of (NPPy)(TCNQ)n
A wide range of electrical, magnetic and structural properties of the organic conductors based on 7,7,8,8,-tetracyanoquinodimethane, TCNQ, have been observed, and these have set up active arguments on their origin and how the physical properties can be designed. (1). We have suggested that substituted pyridinium and thiazolium salts of TCNQ form a unique class of materials serving as a good tool for studying the solid state chemical properties of organic conductors (2,3). In particular, N-n-propylpyridinium(TCNQ)n ((NPPY)(TCNQ)n or A) shows a reversible first-order phase transition at 108°C accompamied with a sudden change in resistivity by a factor upto 20 (2). The high temperature phase is featured by both temperature-independent resistivity of 2 Ωcm and magnetic susceptibility of 6.6 × 10-4 emu/mol. The crystal structure change is supposed to dominate the phase transition, because its nature can be varied strikingly by modifying the structure of the cation molecule. Moreover, the reversible transition is found only for salts having specific cations; e.g., N-n-butylpyridinium(TCNQ)n ((NBPy)(TCNQ)n or B), N-n-propylthiazolium(TCNQ)n ((NPTh)(TCNQ)n or C) and N-n-butyl-thiazolium(TCNQ)n ((NBTh)(TCNQ)n or D) (2,3).
KeywordsPhase Transition High Temperature Phase Domain Wall Motion Active Argument Organic Conductor
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